Under emergency situations, a driver may rapidly depress a brake pedal. However, the driver may not depress the brake pedal sufficiently or the driver may not maintain a sufficient force for a necessary period of time. Thus, to improve vehicle safety, some automatic brake assisting systems have been introduced in the market. Such known brake assisting systems employ a vacuum booster to automatically boost the braking force when the driver depresses the brake pedal rapidly.
Japanese Laid-Open Patent Publication No. H08-230634 published on Sep. 10, 1996, which corresponds to U.S. Pat. No. 5,727,852, discloses a brake assisting system in which a pump for anti-skid control or traction control is also used for boosting the braking force to reduce the role of the vacuum booster. This system includes a wheel cylinder, a master cylinder, a main line connecting the master cylinder to the wheel cylinder, a first valve to open and close the main line, a pump having an inlet port and an outlet port to supply pressurized brake fluid to a point between the first line and the wheel cylinder, an auxiliary line connecting the inlet port of the pump to the master cylinder, and a second valve to open and close the auxiliary line.
This known system also includes a pressure sensor to detect the output pressure from the master cylinder. The pump, the first valve and the second valve perform brake assistance under proper control when the output pressure and the pressure increase ratio exceeds the predetermined value. To increase the pressure, the first valve is opened and the second valve is closed. Then, the pressure increase rate is controlled by turning on and off the pressure pump. However, in this known system, the proper pressure increase rate may not be obtained in accordance with the driver's brake pedal operation when the electric motor keeps turning on.
It may be possible to obtain the proper pressure increase rate by turning on and off the electric motor. However, the pump may not discharge a sufficient amount of brake fluid from the reservoir because the pressure in the reservoir is less than the pressure in the master cylinder under anti-skid control. Accordingly, due to less discharge by the pump, the reservoir may be full so that anti-skid control may not be properly performed.
In light of the foregoing, a need exists for a brake control apparatus that is not susceptible to the foregoing drawbacks and disadvantages.
It would thus be desirable to provide a brake control apparatus that is able to simultaneously perform brake assist control and anti-skid control.
It would also be desirable to provide a brake control apparatus that is able to increase the brake pressure in a wheel cylinder immediately after initiation of brake assist control.
It would be further desirable to provide a brake control apparatus that is able to control the brake pressure in a wheel cylinder according to a driver's brake operation.